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An NFA is represented formally by a 5-tuple, (Q, Σ, Δ, q0, F), consisting of

1. a finite set of states Q
2. a finite set of input symbols Σ
3. a transition function Δ : Q × Σ → 2Q
4. an initial (or start) state q0 ∈ Q
5. a set of states F distinguished as accepting (or final) states F ⊆ Q.